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Biomedical subjects

R W Blake

Publications and source records attributed to R W Blake.

14 recordsLinked to original sources
PubMed1994

Economic comparison of nutritional management strategies for Venezuelan dual-purpose cattle systems.

Objectives of this study were to compare three nutritional management strategies for dual-purpose herds in Venezuela in 1987 using a deterministic, multiperiod linear programming model of a representative farm. The model maximized discounted net margin (total revenues minus variable costs) from the herd for a 3-yr cow replacement cycle partitioned into six periods. The periods accounted for seasonal variation in forage availability and quality, and the model provided information about optimal animal inventories, animal sales, land in forage, and feed supplements. We compared current nutritional management practices and alternatives allowing optimal supplementation with commercial concentrate, molasses, cassava root, and urea. Iteration between the programming model and results from the Cornell Net Carbohydrate and Protein System assured technical coefficients consistent with predicted animal performance. Compared with management practices relying on commercial concentrate, optimal use of molasses and urea permitted increases in the stocking rate. Productivity and profit were restricted primarily by energy intake, which was constrained by intakes of NDF and DM. Alternative management strategies changed the relative importance of nutrient requirements and feed intake constraints. Thus, optimal interventions to alleviate nutritional constraints will vary with current management. Mobilizing adipose and protein tissues during lactation was optimal for most strategies. Supplementing with molasses and urea instead of commercial concentrate was the most profitable strategy, increasing herd net margin by 16% compared to the predominant feeding strategy in the late 1980s.

Adipose Tissue↗
PubMed1991

Skeletal muscle deformation in the lateral muscle of the intact rainbow trout Oncorhynchus mykiss during fast start maneuvers.

Although there is an extensive body of information on the kinematics of the fast start response in teleosts, there is little information on the deformation of the skeletal muscle which produces the changes in body position during a fast start. This study presents preliminary information on the determination of skeletal muscle deformation with implanted ultrasonic dimension gauges in the intact fish during startle behavior. Deformation was measured in the lateral epaxial musculature of the rainbow trout Oncorhynchus mykiss during stage one of fast starts. The results show that ultrasound transit time dimension gauges can be implanted in the skeletal muscle of rainbow trout with minimum trauma and used to record local deformation along the length of the fish. Measurements remained stable over 4-8 h of implantation. Preliminary results show that: (1) muscle at different positions along the fish reaches its minimum length (average 9.6% shortening) at approximately the same time and coincident with the end of stage one of the fast start response; (2) the onset of concave curvature of the entire fish precedes the onset of local shortening at more caudal sites; (3) muscle on the convex side of a bend lengthens while muscle on the concave side shortens, and the two deformations follow a similar time course. These results indicate an asynchronous onset of skeletal muscle contraction in fast starts and support the hypothesis that local skeletal muscle deformation is transmitted caudally through skeletal or other structures.

Animals↗
PubMed1991

Genotype by environment interaction for Holstein milk yield in Colombia, Mexico, and Puerto Rico.

Components of (co)variance and genetic parameters were estimated by REML procedures from first lactation mature equivalent Holstein milk records from 54,604 Colombian, Mexican, and Puerto Rican cows and 198,079 US cows. The objective was to determine the cause of heterogeneous daughter response to sire selection for milk yield between the regions. Data from Latin America were partitioned by country and by herd-year SD class for milk to obtain five joint analyses between the US and Latin America, low herd-year SD, high herd-year SD, Colombia, and Mexico. Sire and residual variances for milk were 41 and 29% smaller in Latin America than in the US, 47 and 58% smaller for low than for high herd-year SD, and 31 and 49% smaller for Colombia than for Mexico. Resultant heritabilities ranged from .20 to .29. Genetic correlations for milk yield between the US and Latin America, low and high herd-year SD, Colombia, and Mexico were .91, .82, .89, .78, and .90. Expected correlated responses for milk in Latin America, low and high herd-year SD, Colombia, and Mexico were 70, 53, 79, 56, and 78% of the direct response in the US. The scaling effects of heterogeneous variance resulted in smaller daughter milk responses in Latin America compared with the US even when herd-year SD was similar.

Animals↗
PubMed1989

Effects of age, parity, season of calving, and sire on milk yield of Carora cows in Venezuela.

Age-parity-season of calving, mature equivalent factors were developed for the Carora breed of Venezuela from more than 13,000 244-d milk yield records from the Venezuelan milk recording program from 1975 to 1986. Age-parity-season interactions with parity-age were most important for young cows and seasonal effects most important for old cows. Multiplicative factors were verified as useful to adjust milk yields of Carora and Brown Swiss crossbred cows. Repeatabilities for mature equivalent adjusted milk were .47, .36, and .38 between pairs of repeated records through fourth lactation. Heritability of milk in first lactation by REML procedures was 12% based on 44 Carora sires with 14 effective daughters per sire. Small population size for Carora cattle hinders usefulness and cost effectiveness of progeny testing as the primary investment in genetic gain. Greater potential economy is likely from exploiting the dams of sires genetic pathway.

Age Factors↗
PubMed1987

Economic evaluation of fourteen methods of estrous detection.

Costs of 14 methods to detect estrus were compared under simulated commercial dairy situations using artificial insemination. Alternative methods were twice or thrice daily visual observation and factorial combinations with various estrous detection aids [teaser bull, heat mount detector, and tail paint (also in combination with visual observation only during routine chores), estrous synchronization by prostaglandin F2 alpha, estrous synchronization plus heat mount detector]. A sensitivity analysis was used to compare tail paint and heat mount detector methods. Total costs for labor and other inputs were estimated for alternative 120-cow dairy herds with cumulative conception rate greater than or equal to 90% by considering five labor wage rates, four first-service conception rates, and three detection rates for each estrous detection method. Heat mount detector and tail paint methods with visual observation only during routine dairy chores always had lowest cost when average wage rate exceeded @2.25/h. To make heat mount detectors competitive, corresponding detection rate would have to be at least 10% higher than for the tail paint method. Unaided visual observation with two checks/d was less expensive than heat mount detector methods when labor had few alternative demands and cost less than $2.25/h. These methods were generally less than half as costly as teaser bull and prostaglandin alternatives.

Animal Husbandry↗
PubMed1987

Commercial feasibility of embryo transfer technology: a case study.

The owner of a 500-cow Holstein herd requested economic assessment of his embryo transfer program. Actual net economic benefit was determined from marginal cost and present value of lifetime milk predicted from first lactations of 24 cows produced by embryo transfer compared with those of their 51 contemporaries sired by artificial insemination. Actual average pregnancy rate was 60% by embryo transfer or AI. An average of 5.5 transferable embryos was obtained per collection, which produced 1.37 cows in first lactation. Additional milk from embryo transfer cows was from more intensive selection of sires. Additional milk from the donor cows did not differ from zero. Actual marginal cost of a replacement by embryo transfer was +215, but it would have been +200 with same +25/unit semen price as contemporaries. If donors had been from the elite 5% for transmitting ability in milk, present value of gain in milk (5% real interest rate) ignoring additional feed costs would have been less than the cost of embryo transfer. For management and costs similar to this case, embryo transfer is not economically justified for producers earning income primarily from the sale of milk.

Animal Husbandry↗
PubMed1986

Genetic methods of improving dairy cattle for the south: a review and prospects from Regional Project S-49.

Objectives of Southern Regional Research Project S-49, comprising eight contributing experiment stations, are to determine direct response to selection in milk and the resultant correlated responses in nonyield traits, to define and evaluate selection criteria for total economic merit or profit, to quantify genetic and environmental components of underlying physiological characters responsible for genetic gains in economically important traits, to determine interactions of genotype by environment, and to estimate genetic values for males and females. More than 150 scientific articles from S-49 have been published in journals from 1975 to 1985. These results have contributed in a major way in identifying issues and understanding the genetic control of cow performance and economics of genetic improvement programs.

Animals↗
PubMed1986

Comparative feed efficiency of Holstein and Jersey cows.

Feed efficiency measures, gross energy (solids-corrected milk/estimated energy intake), N (milk N/N intake) utilization, and apparent digestibilities of ration dry matter and N were calculated for 34 daughters of 21 Holstein and 29 daughters of 18 Jersey sires in first and second trimesters of lactation. Cows were studied in N balance trials and were fed ad libitum corn silage-based, complete rations formulated to meet average nutrient requirements. The objective was to determine whether these breeds differ in rates of converting dietary protein or energy to milk protein or milk energy. Holstein and Jersey did not differ for digestibility of ration dry matter in either trimester of lactation. They also converted dietary protein to milk protein at similar rates. Energy efficiencies of Holstein and Jersey did not differ in first trimester, but Holstein exceeded Jersey in second trimester. Because intake of dry matter by Jersey increased about 4% from first to second trimester (opposite of Holstein) and N balance was higher than for Holstein, Jersey cows may have been repleting more adipose tissue. We suggest no comparative advantage for Jersey in spite of higher ratios of milk to body weight and feed intake less than Holstein.

Animals↗
PubMed1984

Considerations in multiple trait evaluation.

Traits of dairy cattle known to contribute to genetic merit are discussed briefly. Focus is on alternative measures and research to reflect more closely genetic pathways of performance because knowledge is expanding about cellular, organ, and animal function. Improved measurement of physiological traits of economic characters portends increased genetic control of animal productivity by considering more alternative traits. Research should clarify multiple trait selection programs to maximize profit. The null hypothesis to test is that selection for milk is optimal index selection for milk income and costs of production.

Animal Feed↗
PubMed1984

Ovarian activity of Holstein and Jersey cows of diverse transmitting abilities for milk.

The relationship between ovarian activity and milk yield was studied in 35 daughters of 24 Holstein sires and 17 daughters of 14 Jersey sires in the same herd. Ovulations and length of estrous cycles were determined by progesterone concentration in postmilking strippings three times per week, by weekly palpation per rectum, and by twice daily estrus detection. Transmitting abilities were for 4% fat-corrected milk of cows and their sires. Yields of 4% fat-corrected milk were estimated for 60, 90, 120, and 305 days in lactation. Postpartum intervals to first ovulation averaged 22 and 20 days for Holsteins and Jerseys, but the interval to first standing estrus was shorter for Jersey than for Holstein. Postpartum intervals to each of the first three ovulations and length of estrous cycles were unrelated to actual yield or transmitting ability for yield of 4% fat-corrected milk in either breed. The percentage of cows observed in standing estrus at each of the first three ovulations increased from 23 to 43%.

Animals↗
PubMed1983

Mechanics of gliding in birds with special reference to the influence of the ground effect.

A model of the mechanics of gliding without loss of altitude (horizontal gliding) is developed. The model can be employed to assess the influence of the principal drag components (induced, profile and parasite drag), choice of initial and final glide velocities and height above the ground on glide distance. For birds gliding near to the ground the ground effect acts to decrease the induced drag and increase the lift to drag ratio of the wings. Minimum drag speed is reduced for birds gliding near to the ground. The model is applied to the gliding flight of the black skimmer (Rhyncops nigra). Glide distances for given initial and final velocities are significantly increased in the influence of the ground effect over out of ground effect values.

Aerospace Medicine↗
PubMed1983

Relationships between measures of feed efficiency and transmitting ability for milk of Holstein cows.

Feed efficiency measures, gross energy (solids-corrected milk/estimated energy intake) and nitrogen (milk nitrogen/nitrogen intake) utilization, and apparent digestibilities of ration dry matter, nitrogen, acid detergent fiber, and starch were calculated for 134 samples of 75 daughters of 31 Holstein sires. Cows were in 5- to 9-day nitrogen balance trials in first and second trimesters of lactation and were fed for ad libitum consumption corn silage-based complete rations formulated to meet average nutrient requirements. The objective was to test the hypothesis that feed efficiency diminishes as milk increases from selection. The sample of cows closely approximated the distribution of genetic ability for milk of the Holstein breed. Nonsiblings of same parity (one, two, three or more), calving within 2 wk of each other and differing by at least 140 kg estimated transmitting ability, were paired in nitrogen balance trials. Evidence for diminishing returns to increased transmitting ability for milk was nil for any measure of feed efficiency. Energy efficiency showed linear increases when regressed on cow transmitting ability for fat-corrected milk, but other measures of dietary utilization were unrelated to milk yield.

Animals↗
PubMed1982

Milk production of quarter horse mares during 150 days of lactation.

Milk production was measured in fourteen Quarter Horse mares at seven stages of a 150-d lactation period. Mares were divided into two groups of seven and fed diets containing either soybean meal or soybean meal and urea as nitrogen supplements. Rations were isocaloric, contained approximately 12.5% crude protein and were fortified with vitamins and minerals. Daily milk yield was estimated by the weigh-suckle-weigh method and milk composition was determined from samples taken by hand milking. Average daily milk yield ranged from 11.8 kg in early lactation to 9.8 kg in late lactation. Differences (P less than .01) in milk yield due to number of previous lactations were observed. Also, diet influenced (P less than .01) milk yield, with mares fed soybean meal producing an average of 1.2 kg more milk/d than mares fed urea as part of the N supplement. Further, stage (day) of lactation influenced (P less than .01) daily milk yield. The largest mean daily milk yield was measured at approximately 30 d postpartum, but the predicted lactation curve was linear (P less than .05) over the range of observations in this study. Average percentages of total solids, protein and fat over the 150-d lactation were 10.5, 2.1, and 1.3, respectively. All components decreased significantly with advancing lactation. There was a trend toward a positive association between milk yield and solids content of the milk, but it was not significant. Milk yield was not significantly related to fat content of the milk. However, milk yield and protein content were correlated (r = .23; p less than .05). As expected, solids content of the milk was positively associated with percentages of protein (r = .59; P less than .01) and fat (r = .44; P less than .01). Relationships among milk components were similar after adjustment for days in milk. However, yield of milk and composition were unassociated (P less than .05) when days in milk were held constant.

Animals↗